Can be used alone, or in combination with early_period_in_days to provide an early payment discount. When used as an early discount, the percentage is multiplied by early_period_in_days - so you can define a discount of "1% every 5 days paid early", etc.
Floating point value. Specified as a percentage.

document_template_id

ID of the document_template used to display this invoice.

due_date

Date this invoice is due for payment.

early_period_in_days

Defines the number of days before due_date that discount_percentage is applied, if you wish to use an "early payment" discount.

has_been_paid

True if invoice is paid, false if not.

has_been_sent

Will be set to true if it has been emailed via the system.
May also be set manually if customer post-mails their invoices.

include_expenses

Controls the visibility of associated expenses when rendering to HTML or PDF.

include_pdf

Determines if a PDF file should be included when sending reminder notifications

include_time_entries

Controls the visibility of associated time entries when rendering to HTML or PDF.

invoice_date

The date this invoice was issued to the client.

item_actual

Dollar amount of all line_items, including markup_percentage.

item_cost

Dollar amount of all line_items, before markup_percentage.

item_profit

Dollar amount made via markup_percentage on all line items.

item_taxable

Dollar amount of items that are marked taxable.

late_fee

Dollar amount assessed for late payments.

late_percentage

Similar to discount_percentage, but applies a late payment fee instead.
Used in combination with late_period_in_days.
late_percentage will be applied every late_period_in_days after due_date.
Floating point value. Specified as a percentage.

late_period_in_days

Defines the number of days after due_date that late_percentage is applied, if you wish to use late payment fees.

notes

Custom notes field that is shown on the invoice to your clients.

payment_total

Dollar amount of payments that have been made against this invoice.

post_reminder_in_days

Every X days after due_date the invoice is unpaid an email notification will be sent to your client.

pre_reminder_in_days

Every X days before due_date the invoice is unpaid an email notification will be sent to your client.

sales_tax

Floating point value. Specified as a percentage.

sales_tax_2

Floating point value. Specified as a percentage.

sales_tax_cumulative

Boolean. Determines if sales_tax_2 is a compound tax, including sales_tax